Prevent self-inspection from leaking configured secrets

MyTool blocks direct access to sensitive nested paths, but its formatter
still printed scalar fields for small config objects. That let
`my(action="check", key="web_config.search")` expose `api_key` in plain
text even though the docs promise sensitive sub-fields are protected.

This keeps the change narrow: sensitive nested config fields are omitted
from MyTool's formatted output, and regression coverage locks the
behavior in.

Constraint: Must preserve existing read-only inspection behavior for non-sensitive fields
Constraint: Keep scope limited to MyTool rather than introducing broader redaction plumbing
Rejected: Rework global context/tool redaction around MyTool | broader than needed for the leak path
Confidence: high
Scope-risk: narrow
Reversibility: clean
Directive: If more nested config rendering is added later, filter sensitive field names at the formatter boundary as well as the path resolver
Tested: PYTHONPATH=$PWD pytest -q tests/agent/tools/test_self_tool.py /Users/jh0927/Workspace/nanobot-validation-artifacts-2026-04-18/test_my_tool_secret_leak_regression.py
Not-tested: Full repository test suite
Related: #3259

nanobot/agent/tools/self.py

@@ -67,6 +67,13 @@ class MyTool(Tool):
         "private_key", "access_token", "refresh_token", "auth",
     })
 
+    @classmethod
+    def _is_sensitive_field_name(cls, name: str) -> bool:
+        lowered = name.lower()
+        return lowered in cls._SENSITIVE_NAMES or any(
+            part in cls._SENSITIVE_NAMES for part in lowered.split("_")
+        )
+
     RESTRICTED: dict[str, dict[str, Any]] = {
         "max_iterations":        {"type": int, "min": 1,   "max": 100},
         "context_window_tokens": {"type": int, "min": 4096, "max": 1_000_000},
@@ -248,13 +255,16 @@ class MyTool(Tool):
             return f"{key}: {r}" if key else r
         # Complex object — small Pydantic models: show values; others: show field names for navigation
         cls_name = type(val).__name__
-        if hasattr(val, "model_fields"):
+        model_fields = getattr(type(val), "model_fields", None)
-            fields = list(val.model_fields.keys())
+        if model_fields:
+            fields = list(model_fields.keys())
             if len(fields) <= 8:
                 # Small config objects: show field=value pairs
                 pairs = []
                 for f in fields:
                     fv = getattr(val, f, "?")
+                    if MyTool._is_sensitive_field_name(f):
+                        continue
                     if isinstance(fv, (str, int, float, bool, type(None))):
                         pairs.append(f"{f}={fv!r}")
                     else:

tests/agent/tools/test_self_tool.py

@@ -7,6 +7,7 @@ from pathlib import Path
 from unittest.mock import AsyncMock, MagicMock
 
 import pytest
+from pydantic import BaseModel
 
 from nanobot.agent.tools.self import MyTool
 
@@ -168,6 +169,25 @@ class TestInspectPathNavigation:
         result = await tool.execute(action="check", key="tools")
         assert "not accessible" in result
 
+    @pytest.mark.asyncio
+    async def test_inspect_nested_config_redacts_sensitive_scalar_fields(self):
+        class SearchConfig(BaseModel):
+            provider: str = "tavily"
+            api_key: str = "sk-test-secret"
+            base_url: str = ""
+            max_results: int = 5
+
+        loop = _make_mock_loop()
+        loop.web_config = MagicMock()
+        loop.web_config.search = SearchConfig()
+        tool = _make_tool(loop)
+
+        result = await tool.execute(action="check", key="web_config.search")
+
+        assert "provider='tavily'" in result
+        assert "sk-test-secret" not in result
+        assert "api_key" not in result.lower()
+
 
 
 # ---------------------------------------------------------------------------